Construction crews work at a house in Vallejo, Calif., after a deadly fire, Aug. 5, 2018.
(Associated Press)

A fire at a home in the San Francisco Bay Area this week that killed a mother and her 14-year-old twin daughters started when the mother deliberately set herself ablaze, police said Thursday.

Evidence at the scene as well as information gathered from witnesses showed that Mau Dao, 47, committed an act of self-immolation at her home in Vallejo, about 32 miles north of San Francisco, the Bay Area’s FOX 2 reported.

The blaze, which started around 2:45 a.m. Sunday, also killed twins Trinh and Tram Tran, who were about to become high school sophomores, the report said.

One teen died at the scene, while the other teen died in a hospital and their mother died in a burn unit, FOX 2 reported.

The twins’ 11-year-old sister was injured in the fire, but managed to escape from the home. A police officer on patrol spotted the girl, who told him the others were still inside the home, but the fire by then was too intense.

The 11-year-old was expected to make a full recovery and was staying with her father, the Associated Press reported.